Pseudomonas aeruginosa is an important opportunistic pathogen of humans that is notorious for being the principal cause of morbidity and mortality in Cystic Fibrosis (CF) patients. In the chronically infected CF lung the organism persists as a biofilm-a surface attached community of bacteria encased in a polymeric matrix. This biofilm mode of growth augments the resistance of P. aeruginosa to antibiotics and facilitates evasion of the host immune response. We have uncovered an essential transcription regulator in P. aeruginosa (encoded by the PA0906 gene) that we have implicated in biofilm formation. We have found that the essential function of this regulator is to prevent cell lysis by repressing the expression of the PA0907 gene. The PA0907 gene encodes another regulator that in turn positively controls the expression of a set of genes that contributes to cell lysis. T begin to define the regulatory cascade that is triggered by the loss of PA0906, we have taken advantage of the fact that this protein belongs to a well-studied family of regulators that undergo cleavage in response to DNA damage. In particular, comparison of wild-type cells with cells containing an uncleavable PA0906 mutant enabled us to identify ~30 genes that are subject to control by this regulator. In addition we have found that cleavage of PA0906 is important for biofilm formation in vitro. Here we propose to (i) determine which genes are subject to direct control by PA0906 and which genes are subject to direct control by PA0907, (ii) identify PA0907-controlled genes that contribute to cell lysis, (iii) test whether or not PA0906 influences biofilm formation in a CF-airway epithelial cell model and (iv) determine how PA0906 influences biofilm formation. Our studies are expected to reveal the basis for the essentiality of a previousl uncharacterized transcription regulator and illuminate the role this regulator plays in the control of biofilm formation. Because the regulator that is the focus of these studies is essential, and thus a potential antibiotic target, it is possible that the work we propose could help in the development of novel therapeutics for the treatment of CF patients.